An extended clip from Avengers: Endgame using the concept of time travel to create a host of alternate realities.
The the Elemental creatures wreaking havoc across Europe are also from another reality. The jury's out as to whether or not Mysterio is telling the truth, of course; in the comics, the sorcerer pretended to be a superhero on his first appearance. Assuming he is, though, the multiverse opens up a whole host of new opportunities for the MCU.
An extended clip from Spider-Man: Far From Home was aired on Ellen, showing Peter Parker's full introduction to Quentin Beck. In it, Beck gives a little more information about the multiverse. He claims that the MCU is "Earth-616," and that he originates from "Earth-833." Mysterio sounds to be quite used to the idea of jumping between dimensions, claiming that Earth-616 and Earth-833 "share identical physical constants, Level 4 symmetry."
These references will be very familiar to comic book readers. Earth-616 is the traditional designation for the main Marvel Comics universe. It was first used in 1983 by Alan Moore in one of the Marvel UK comics, in order to differentiate between the mainstream Captain Britain and the other of the multidimensional Captain Britain Corps. It was later adopted by Chris Claremont in his Excalibur run, and gradually became standard across Marvel. In 2015, the multiversal "Secret Wars" event led to the destruction of the entire Marvel Multiverse, which was ultimately restored by the Fantastic Four. Earth-616 became Ground Zero for the creation of the new multiverse, and as a result was rechristened Prime Earth.
According to Mysterio, the Marvel Cinematic Universe is Earth-616. This is actually the second time Earth-616 has been mentioned in the MCU; Erik Selvig scrawled the words on his chalk-board in Earth-199999," but that's never been said on the big screen.
Meanwhile, Mysterio claims to come from Earth-833. This, too, is a familiar designation to comic book readers; it's the home universe of Spider-UK, an alternate-reality Spider-Man who left his dimension in order to serve as a member of the Captain Britain Corps.
Update (May 7): We've adjusted title and text to better reflect the previous designation number of the MCU.
Source: Ellen
